Thermotropic liquid crystalline polymers (LCPs) are important items of commerce. They are particularly noted for their good melt forming characteristics, often low flammability, and in many cases usefulness at higher temperatures. One goal with LCPs has been to develop polymers with higher and higher temperature capabilities.
Polyester LCPs derived from hydroquinone (HQ), terephthalic acid (TA), 2,6-naphthalenedicarboxylic acid (NDA), 4-hydroxybenzoic acid (HBA) are known, see for instance U.S. Pat. Nos. 4,169,933, 6,121,369 and 6,306,946. In all of these references the LCPs actually made had relatively (compared to the LCPs described herein) high amounts of repeat units derived from terephthalic acid in them.
In particular, U.S. Pat. No. 6,306,946 reports the variation of certain properties of the LCPs with changes in polymer composition. In FIG. 8 of this patent the variation of Heat Deflection Temperature (HDT) with polymer composition is given in the form of a contour plot and an equation to predict HDT as a function of polymer composition. HDT is a property that is often used to predict the (relative) usefulness of polymers at higher temperatures. In essence it measures the stiffness (more accurately the resistance to bending) of a polymer as the temperature is increased. Usually the higher the HDT, the higher the temperature the polymer may be used in any given use. The LCPs described herein surprisingly have much higher HDTs than are predicted by the equation at the bottom of FIG. 8(Equation C) of U.S. Pat. No. 6,306,946.
U.S. Pat. No. 4,067,852 discloses polymers having repeat units derived from hydroquinone, 2,6-naphthalenedicarboxylic acid and 4-hydroxybenzoic acid. The only example of such a polymer reported in this patent contains a much higher level of repeat units derived from 4-hydroxybenzoic acid than the polymers claimed herein.